This application is based upon and claims the benefit of priority of the prior Japanese Patent Application 2003-280963 filed on Jul. 28, 2003.
The present invention relates to a control apparatus for an internal combustion engine that calculates a requisite time required for a crank shaft of an internal combustion engine to rotate from a present crank angle to a designated crank angle where the control apparatus controls a predetermined device of this engine.
For example, Japanese Patent Application Laid-open No. 08-338349 (1996) discloses a conventional control apparatus for an internal combustion engine that variably controls power supply time for ignition coils in an ignition device in accordance with driving conditions of the internal combustion engine. More specifically, the control apparatus changes the power supply time for the ignition coil in accordance with the temperature of the ignition coil. This is effective in assuring proper ignition performance regardless of temperature changes occurring in the ignition coils, as well as in ensuring a long life for respective transistors that control the output of ignition coils.
The above-described ignition device controls the power supply time for determining the current supplied to each ignition coil and also controls an ignition timing at which the current supplied to the coil is stopped. More specifically, the ignition timing is set to a predetermined timing. The power supply to each ignition coil starts from a timing advanced a required power supply time from the predetermined ignition timing. The power supply to each ignition coil terminates at the ignition timing. The ignition timing is designated as a crank angle. A crank shaft of the engine rotates from the present crank angle to a crank angle corresponding to the ignition timing. A requisite time is calculated as a time required for the crank shaft to rotate from the present crank angle to the crank angle corresponding to the ignition timing. Usually, the requisite time is calculated with reference to past rotational speeds of the crank angle. The requisite time being thus calculated will be adversely effected by changes of the rotational speed of the crank shaft, occurring due to acceleration, deceleration, combustion cycle, or the like of an internal combustion engine. In view of the above, to accurately perform the ignition timing control, the control apparatus for a conventional internal combustion engine gives a sufficient margin for the above-described power supply time. In other words, the conventional engine control is the one giving priority to the ignition timing control.
Hereinafter, setting of the above margin will be explained with reference to FIGS. 14 and 15. FIG. 14 shows a conventional ignition timing control in an accelerating condition. FIG. 15 shows a conventional ignition timing control in a decelerating condition. In each of FIGS. 14 and 15, (a) represents a crank signal, (b) represents a calculated ignition output at a crank angle BTDC70, (c) represents a calculated ignition output at a crank angle BTDC40, and (d) represents a current value supplied to an ignition coil. In this description, BTDC stands for ‘before top dead center’.
In each of FIG. 14 and FIG. 15, the ignition timing is assumed to be in a crank angle range from BTDC40 to BTDC10. As shown in FIGS. 14(b), 14(c), 15(b), and 15(c), the ignition timing and the power supply start time for predetermined crank angles BTDC70 and BTDC40 are calculated based on measured times α and β required for the crank shaft to rotate a preceding 180 CA (crank angle). In this case, accurately executing the above-described ignition timing control is feasible by calculating the ignition timing at the crank angle of BTDC40. Meanwhile, calculating the ignition timing at the crank angle BTDC70 is effective in assuring a sufficient power supply time.
As shown in FIG. 14, when the internal combustion engine is in the accelerating condition, the measured time β is shorter than the measured time α. The measured time α is used for calculating the ignition timing at the crank angle BTDC70. The measured time β is used for calculating the ignition timing at the crank angle BTDC40. The ignition timing being newly set at the crank angle BTDC40 is earlier than the ignition timing being effective at the crank angle BTDC70. As a result, the power supply time becomes short. Under such circumstances, a margin is necessary to secure a sufficient power supply time. However, setting the margin considering these circumstances will raise a problem in the decelerating condition shown in FIG. 15 such that the power supply time becomes excessively long compared with a proper power supply time.
Regarding the power supply amount (i.e. required current pulse width) for an ignition coil, there is a lower limit and an upper limit as shown in FIGS. 14 and 15. Elongating the power supply time as described above may cause a problem such that the current supplied to the ignition coil may exceed a required current pulse width. Accordingly, in the case that the current supplied to the ignition coil exceeds the required current pulse width, the current supplied to the ignition coil is regulated by a specific hardware (e.g., regulator). However, the above-described required current pulse width is dependent on characteristics of each ignition coil. It will be necessary to develop the regulators so as to suit individual ignition coils. The cost for manufacturing the control apparatus will increase. A long developing time will be required for the control apparatus.
Furthermore, the surplus of regulated current is converted into thermal energy. The temperature of a portion positioned adjacent to the regulator will increase. Especially, a control apparatus incorporating an ignition module will produce a significant amount of heat from the ignition module which serves as a heat generating source. Suppressing the temperature increase is an important issue to be attained in designing the control apparatus.
Besides the above-described ignition timing control, the conventional control apparatus cannot accurately calculate a requisite time required for the crank shaft to rotate from the present crank angle to a designated crank angle where the control apparatus controls a predetermined device of the engine.